The present invention relates to a plasma processing apparatus for processing a subject like a substrate such as a semiconductor wafer in a processing chamber in a vacuum container, by using plasma, and more particularly to a plasma processing apparatus capable of reducing foreign matters on a processed subject by blocking fine particles inbound from a vacuum pump side to the subject.
In a plasma processing apparatus of this type, a subject is processed generally in a reduced pressure vacuum atmosphere. In the processing apparatus of this type, it is necessary to lower a pressure in a processing chamber to a high vacuum degree when a subject is processed. In order to realize this high vacuum degree; a turbo molecular pump is generally used which is a vacuum pump equipped with a plurality of stages of vanes rotating coaxially.
Reaction products generated during plasma processing for a subject in a processing chamber and fine particles sputtered by plasma are attached to and deposited on a wall surface of the processing chamber. If such subject processing is performed for a long time duration or for a number of subjects, attached and deposited substance accumulated on the inner wall of the processing chamber may be stripped or broken due to a change in a pressure in the processing chamber, a change in a surface temperature, interaction with plasma or the like, so that fine particles are newly formed.
Although some of fine particles formed in this manner are transported to the vacuum pump and removed from the processing chamber, other fine particles are attached to the surface of a subject to form foreign matters. The following phenomenon is also known in this technical field. Fine particles arrived at an inlet opening of the vacuum pump and flying into the inside of the vacuum pump collide against vane wheels coaxially rotating at high speed. Some of collided fine particles are repelled toward the processing chamber and flown in all direction in the processing chamber to attach the surface of the subject to form foreign matters (hereinafter called rebounded contaminating matters). This phenomenon is disclosed, for example, in “Visualization of Reverse Flowing Particles from Turbomolecular Pump” by Shintarou SATOU, Clean Technology, June, 2003 edition, p. 20, Japan Industrial Publishing Co. Ltd.
Techniques of suppressing adverse affects of such rebounded contaminating matters are known as disclosed in JP-A-2007-180467. This related art discloses a method of solving the above-described issue of rebounded contamination matters by disposing a fine particle reflecting member of a circular disc type facing a turbomolecular pump, in an exhaust manifold.